I. Field
The present invention relates generally to communication, and more specifically to data transmission in a multi-antenna communication system that utilizes orthogonal frequency division multiplexing (OFDM).
II. Background
OFDM is a multi-carrier modulation technique that effectively partitions the overall system bandwidth into multiple (K) orthogonal subbands, which are also referred to as tones, subcarriers, bins, and frequency channels. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data. OFDM is widely used in various wireless communication systems, such as those that implement the well-known IEEE 802.1a and 802.11g standards. IEEE 802.1a and 802.1g generally cover single-input single-output (SISO) operation whereby a transmitting device employs a single antenna for data transmission and a receiving device normally employs a single antenna for data reception.
A multi-antenna communication system may support communication for both single-antenna devices and multi-antenna devices. In this system, a multi-antenna device may utilize its multiple antennas for data transmission to a single-antenna device. The multi-antenna device and the single-antenna device may implement any one of a number of conventional transmit diversity schemes in order to obtain transmit diversity and improve performance for the data transmission. One such transmit diversity scheme is described by S. M. Alamouti in a paper entitled “A Simple Transmit Diversity Technique for Wireless Communications,” IEEE Journal on Selected Areas in Communications, Vol. 16, No. 8, October 1998, pp. 1451-1458. For the Alamouti scheme, the transmitting device transmits each pair of modulation symbols from two antennas in two symbol periods, and the receiving device combines two received symbols obtained in the two symbol periods to recover the pair of modulation symbols sent by the transmitting device. The Alamouti scheme as well as most other conventional transmit diversity schemes require the receiving device to perform special processing, which may be different from scheme to scheme, in order to recover the transmitted data and obtain the benefits of transmit diversity.
A “legacy” single-antenna device may be designed for SISO operation only, as described below. This is normally the case if the wireless device is designed for the IEEE 802.11a or 802.11g standard. Such a legacy single-antenna device would not be able to perform the special processing required by most conventional transmit diversity schemes. Nevertheless, it is still highly desirable for a multi-antenna device to transmit data to the legacy single-antenna device in a manner such that greater reliability and/or improved performance can be achieved.
There is therefore a need in the art for techniques to achieve transmit diversity in an OFDM-based system, especially for legacy single-antenna devices.